Different enzymes are categorized as a specific type of hemicellulase--a glucanase, a xylanase or a mannanase, for example--based on an ability to catalyze the hydrolysis of heteropolysaccharides composed of glucan, xylan or mannan, respectively. It is known that enzymes that effect hydrolysis of mannans, such as a galactan or a glucomannan, are produced by various microorganisms, including bacteria and fungi, and that they also occur in some animals and in numerous plants. Among the microorganisms that produce such mannanases are species of Aeromonas, Aspergillus, Streptomyces, Rhodococcus and Bacillus. See 160 METHODS IN ENZYMOLOGY Part A, Sect. II (1988).
Hemicellulases have been employed commercially, for example, in the processing of coffee, chocolate, cocoa, tea and cereals. Processing these foodstuffs with hemicellulases converts them to a more edible form, thereby improving the energy value of the product, and reduces solution viscosity. Hemicellulases have thus been used to clarify fruit juices, to reduce the viscosity of slurries or purees, to liquefy certain cell wall solids and to modify taste. Similarly, hemicellulases have also been employed to mitigate problems associated with the presence of hemicellulose and other minor polysaccharides in pulps and in unprocessed cotton. By the same token, hemicellulose is a problem when it is present in sewage and industrial waste-water treatment, and in fracturing fluids used in the conditioning of oil-bearing well formations.
Some processes involved in commercial applications utilizing hemicellulose are characterized by conditions of high temperatures and high alkalinity. Hemicellulases in general, and mannanases heretofore described in particular, exhibit substantial activity at a pH range of 3-8 and temperatures below 60.degree. C. These enzymes therefore cannot be used to process hemicellulose cost effectively in applications where these conditions are exceeded.
Nonspecific oxidizing chemicals have been employed to degrade hemicellulose in many commercial oil well fracturing solutions in the exceeded conditions. Incomplete degradation of the hemicellulose is effected, however, at all pHs and temperatures. This can prove to be inefficient, at best, thereby increasing processing costs and resulting in marginal usefulness. For example, partial degradation of mannan-based hydraulic gels, either by chemical oxidizers or by enzymes, leaves a residue that cannot be adsorbed into the surrounding formation. This may lead to a situation whereby the residue can coat fracture surfaces, thereby impeding oil exiting the formation. Accordingly, there is a need for a hemicellulase capable of retaining a substantial portion of its activity in conditions of high alkalinity and at temperatures exceeding 60.degree. C. Such an enzyme would permit complete and efficient degradation of hemicellulose and modified hemicellulose under the conditions that prevail in most of the commercial processes involving hemicellulose-based hydraulic gel.